The present invention relates to sheet tobacco used as a sort of shredded filler for cigarettes or filter cigarettes, and a process and system for manufacturing such sheet tobacco.
In general, sheet tobacco of this kind is produced by a rolling process, a papermaking process or a process using slurry as an intermediate. Each of these processes has its own merits and demerits; however, whichever process is employed, the sheet tobacco obtained has low expansion coefficient.
Examined Japanese Patent Publication (KOKOKU) No. 56-19225 discloses a process for manufacturing sheet tobacco with high expansion coefficient. This conventional process utilizes techniques for producing nonwoven fabric. Specifically, first, a sheet-like mat is formed using a fibrous tobacco material, and the formed mat is then impregnated with a liquid binder to obtain sheet tobacco.
To make use of the above techniques for producing nonwoven fabric, the tobacco material to be used must be of fibers longer than a certain length. Thus, only fibers obtained from stalks and stems of tobacco plant can be used as the tobacco material, and small pieces of shredded tobacco, fragments thereof, etc. produced in the process of manufacture of cigarettes or filter cigarettes practically cannot be reused as the tobacco material.
An object of the present invention is to provide sheet tobacco which can enhance the reusability of tobacco material and has high expansion coefficient, and a process and system for manufacturing such sheet tobacco.
Sheet tobacco according to the present invention has a two-layer structure including a tobacco powder layer and a carrier layer covering one side of the tobacco powder layer and made of nonwoven plant fibers, the tobacco powder layer containing a tobacco powder material and a binder.
The sheet tobacco of the present invention may further include a cover layer. The cover layer is made of nonwoven plant fibers and covers the other side of the tobacco powder layer. In this case, the sheet tobacco has a three-layer structure wherein the tobacco powder layer is sandwiched between the carrier layer and the cover layer.
The carrier layer and the cover layer serve to increase not only the expansion coefficient of the sheet tobacco but the mechanical strength of same. As the powder material of the tobacco powder layer, fine powder which is obtained from small pieces of shredded tobacco and fragments thereof produced in the process of manufacture of cigarettes or filter cigarettes can be used. The sheet tobacco of the present invention can therefore greatly enhance the reusability of the tobacco material.
Preferably, the tobacco powder layer has a basis weight of 30 to 200 g/m2, and the carrier layer and the cover layer each have a basis weight of 3 to 50 g/m2. Also, the content ratio of the binder, for example, cornstarch, to the tobacco powder material in the tobacco powder layer is preferably not greater than 15% by weight. The layers having such basis weights and the binder content impart sufficient original smoking taste and flavor to the sheet tobacco.
The binder is preferably used not only to bind the powder material of the tobacco powder layer, but also to bind together the plant fibers used in the carrier layer and/or the cover layer. In this case, no other binder needs to be used for the plant fibers, making it possible to reduce the binder content in the sheet tobacco.
The sheet tobacco according to the present invention may further include a layer of tobacco particles. The tobacco particle layer contains particles of tobacco stems and laminas and is sandwiched between the carrier layer and the tobacco powder layer or between the tobacco powder layer and the cover layer.
A sheet tobacco manufacturing process according to the present invention comprises: a preparing step of preparing a carrier sheet of nonwoven plant fibers; a forming step of spreading a tobacco powder material on the carrier sheet to form a tobacco powder layer covering one side of the carrier sheet; an adding step of adding a binder to the tobacco powder layer during or after the forming step; and a binding step of binding the powder material in the tobacco powder layer as well as the tobacco powder layer and the carrier sheet to each other by means of the binder.
With the above manufacturing process, sheet tobacco with a two-layer structure is obtained which includes the tobacco powder layer and the carrier sheet as the carrier layer.
Preferably, the carrier sheet is formed by a dry nonwoven fabric production process, and the tobacco powder layer is formed on the carrier sheet continuously following the formation of the carrier sheet. This procedure permits the binder in the tobacco powder layer to be used also to bind together the plant fibers in the carrier sheet.
Since the carrier sheet is formed by a dry process as mentioned above, the quantity of water used in the formation of the carrier sheet is small. Accordingly, the cost of drying the carrier sheet can be reduced, and also the carrier sheet can be prevented from being deteriorated in smoking taste and flavor due to the drying.
After the tobacco powder layer is formed, a cover sheet made of nonwoven plant fibers, like the carrier sheet, may be formed on the tobacco powder layer. In this case, the sheet tobacco has a three-layer structure wherein the tobacco powder layer is sandwiched between the carrier sheet and the cover sheet.
Preferably, the cover sheet on the tobacco powder layer also is formed by a dry nonwoven fabric production process continuously following the formation of the tobacco powder layer.
In the aforementioned binding step, the binder added to the tobacco powder layer serves to bind together the plant fibers in the carrier sheet and the cover sheet. Thus, no other binder is required for the carrier sheet or the cover sheet.
Specifically, the aforementioned adding step is performed by adding a binder of powder or liquid form to the tobacco powder layer in the process of formation of the tobacco powder layer. Preferably, the binder contains cornstarch as a main component. Where the binder used is in powder form, the tobacco powder layer and the carrier sheet, as well as the cover sheet, are made to be impregnated with a solvent for the binder, for example, water, prior to the binding step.
The binding step is carried out by pressing the two-layer sheet tobacco constituted by the tobacco powder layer and the carrier sheet or the three-layer sheet tobacco constituted by the tobacco powder layer, the carrier sheet and the cover sheet with heat applied thereto. In the process of the binding step, the binder binds together the powder material in the tobacco powder layer, binds the tobacco powder layer and the carrier sheet to each other, and also binds the tobacco powder layer and the cover sheet to each other. More specifically, in the case where the binder is in powder form, the binder dissolves in the solvent, forming a binder liquid. The binder liquid infiltrates also into the carrier sheet and the cover sheet, and when heated, the solvent of the binder liquid evaporates, so that the plant fibers are bound together by the binder.
The manufacturing process of the present invention may further comprise the step of forming a tobacco particle layer between the carrier sheet and the tobacco powder layer or between the tobacco powder layer and the cover sheet. The tobacco particle layer is made of particles of tobacco stems and laminas.
A sheet tobacco manufacturing system according to the present invention comprises: an endless net conveyor traveling in one direction; an upstream-side forming device for forming a carrier sheet of nonwoven plant fibers on the net conveyor; a powder spreading device for spreading a tobacco powder material on the carrier sheet to form a tobacco powder layer covering the carrier sheet; and a pressing device for heating and pressing the carrier sheet and the tobacco powder layer.
Preferably, a spraying device is arranged on an upstream side of the upstream-side forming device as viewed in the traveling direction of the net conveyor. The spraying device wets in advance the net conveyor with a predetermined liquid, to facilitate the peeling of the sheet tobacco from the net conveyor.
The manufacturing system may further comprise a downstream-side forming device for forming the cover sheet. The downstream-side forming device includes a fiber spreading unit arranged above the net conveyor for spreading plant fibers toward the net conveyor, a mesh conveyor arranged between the fiber spreading unit and the net conveyor, the mesh conveyor sucking thereon the plant fibers spread from the fiber spreading unit to form a cover sheet and transporting the cover sheet toward the net conveyor, and peeling means for peeling the cover sheet from the mesh conveyor to allow the cover sheet on the mesh conveyor to be transferred onto the tobacco powder layer.